It is on Visual Studio end. Whenever you create a file (e.g. class), you should also build the project in VS or manually “Save All”.

For some reason, the team at Microsoft decided that the project files should only be modified in memory and not flush it to the disk. So when you create a new class, the .csproj is not updated (only its memory equivalent is). I stopped counting the number of times I created a file and then decided to commit to SVN or Git and then have a build fail because the .csproj was not modified and committed along with the changes.